See my examples here- If you use proper casing for an item such as [Felsteel Gloves] you'll find the item in the lookup. If you use all lowercase such as [felsteel gloves] you'll also find it. But if you mix upper and lowercase, it won't find the item - such as [Felsteel gloves] you won't find anything.

Here's some screenshots replicating this behavior-

Edit: I should also note that when mix casing for an item such as Felsteel Gloves it works when you capitlize the G on Gloves, but when you replace it with a lowercase g then it doesn't work. That's what the issue is here - hopefully this makes sense!

Hi @boktai1000! Thanks for your consideration, but the behavior you're describing is working as intended.
As can be seen here, on the Curseforge project page, please note the last item — smart case:

Smart casing is fairly common within text interaction tools, since it provides "best of both worlds ™️". It allows you to ignore casing in the majority of cases, but it can still be utilized when additional filtering is necessary. This makes, e.g., filtering by initials very effective. [BNM → Blade of the New Moon; this query would, if treated case insensitively, not provide context-aware auto completions.

With that said, if you prefer queries to always be treated case-insensitively, this can be configured in-game: